After many years of research, there remains a great deal of development on-going within the field of LEDs. The main focus for this development in recent years has been on finding solutions for improved light output or efficiency (increasing the ‘lumen-dollar ratio’). However, increasingly, the greatest costs associated with implementing LED technology in lighting applications are incurred by components utilized by driver mechanisms.
One way of reducing these costs is by integrating driver functionalities within LEDs themselves, thereby avoiding the need to manufacture additional external components to fulfill these driver functions. One function in particular which it is often desirable to integrate is the ability to control the ON/OFF state of an LED via a series switch. Integrating a switch within the LED die would eliminate one part of the need for expensive driver components.
A series switch coupled to an LED may for example be used to control the flow of current to that LED, when it forms one channel of a multi-channel system. By applying a pulse width modulation signal to such a switch, the duty cycle with which the LED is operated can be controlled, and accordingly the perceived brightness. In this way, the color of a multi-channel system may for example be controlled by controlling each channel independently.
A parallel switch coupled to an LED may for example be used to selectively bypass an LED. This may for example be used in a tapped linear driver in which LEDs are bypassed in dependence on the level of the rectified AC mains voltage, thereby avoiding the need for an expensive regulated current driver.
One approach to integrating switch functionality is to incorporate a transistor on the LED die. This however requires the provision of additional semiconductor layers within the die having a specific doping, and this increases the costs of producing such an LED.
Desired therefore is means of integrating switching functionality within an LED chip—thereby reducing the need for external driver components for controlling the ON/OFF state of the LED—without the need for providing additional semiconductor layers, as for example would be needed for integrating a transistor within the chip.